A gimbal bearing assembly provides a pivoted support that allows for the rotation of an object about an axis. One embodiment of a gimbal bearing assembly includes the use of rolling element bearings, and more particularly a pair of angular contact ball bearings configured for use as a matched set. In general, each angular contact ball bearing includes an inner ring, an outer ring, and a plurality of rolling elements disposed between the inner ring and the outer ring. In many applications, the plurality of rolling elements is separated by a plurality of slug separators wherein typically a slug separator is positioned between a pair of rolling elements. Typically, the pair of angular contact ball bearings of a gimbal bearing assembly is configured such that there is no internal clearance in the bearings when properly mounted. Such a pair of angular contact ball bearings is commonly referred to as a “duplexed” pair of bearings and shall be referred to herein generally as a “duplex bearing.” The gimbal bearing assembly may include more than one pair of angular contact ball bearings, that is, more than one duplex bearing. The duplex bearing provides accurate location of a shaft positioned at least partially therein and is designed to meet low torque, high stiffness and corrosion resistant requirements in a combined load application such as a gimbal bearing assembly.
The duplex bearing includes mounting or otherwise joining the pair of angular contact ball bearings to one another. There are three basic mounting methods to accommodate different loading requirements: Back-to-Back (referred to herein as a “B-Type” duplex bearing), Face-to-Face (referred to herein as an “F-Type” duplex bearing), and Tandem (referred to herein as a “T-Type” duplex bearing). Generally, B-Type and F-Type duplex bearings accommodate heavy radial loads, combined radial and thrust loads, reversing thrust loads and moment loads; while T-Type duplex bearings accommodate heavy radial loads and high one-direction thrust loads with minimum axial shaft deflection.
Axial shaft deflection is a measurement of the deviation of an axial reference surface, such as a surface of revolution or an exterior surface of a shaft, noted during one revolution of the shaft. Radial runout refers to a condition where a rotating component does not rotate in a true plane wherein the surface of a rotating component shifts in relation to its rotational axis. In particular, radial runout is a measurement of the variation in a direction perpendicular to the axis of rotation of an indicated surface, such as the exterior surface of the shaft, from a plane surface of revolution. Angular run out refers to a wobbling movement of the axis of rotation of the shaft and is a measurement of angle of the actual motion of the axis of rotation of the shaft. It has three orthogonal components commonly referred to as roll, pitch, and yaw; respectively, rotation about the X-axis (axis of rotation of the shaft), the Y-axis and the Z-axis. Waviness is a measurement of a broadly-spaced component of surface texture. Waviness is distinguished from flatness by its shorter spacing and its characteristic of being typically periodic in nature. In bearing applications, waviness of bearing races causes vibrations, noise and wear. The Annular Bearing Engineering Committee (“ABEC”), a division of the American Bearing Manufacturers Association (“ABMA”), has adopted an industry accepted standard for specifying the tolerances of a ball bearing. It is known as the ABEC scale and includes five classes from largest to smallest tolerances: 1, 3, 5, 7, and 9. For example, the tolerances of a ball bearing may be specified as ABEC-7T; wherein the “7T” identifies a precision class bearing in accordance with other standards adopted by the ABMA.
Standard rolling element bearings, and in particular duplex bearings, are fabricated such that there is a light axial pre-load induced on the bearing at nominal conditions. In some applications, increased bearing stiffness is provided by inducing a heavier axial load in the mounted bearing. Moreover, the axial load can be increased or decreased to meet the requirements of a particular application. However, typical rolling element bearings known in the art do not necessarily meet the requirements of a gimbal bearing application that has particularly stringent performance goals such as, for example, low starting and running torque, radial run-out and high stiffness characteristics.